PBDB Taxon

Basic info	Taxonomic history	Classification	Included Taxa
Morphology	Ecology and taphonomy	External Literature Search	Age range and collections

Acila (Truncacila) decisa

Bivalvia - Nuculida - Nuculidae

Taxonomy

Nucula decisa was named by Conrad (1855). Its type specimen is UCMP 31132 (neotype) and is a 3D body fossil.

It was recombined as Acila (Truncacila) decisa by Turner (1938), Moore (1983), Squires (1984), Squires (1987), Squires (1988) and Squires (1999).

Sister species lacking formal opinion data

A. ashiyaensis, A. elongata, A. minima, A. piura, A. elongata, A. ermani, A. gottschei, A. marujamensis, A. nakazimai, A. picturata

Synonyms

Nucula (Acila) stillwaterensis was named by Weaver and Palmer (1922). Its type specimen is UW (unknown number), a shell, and it is a 3D body fossil. Its type locality is UW 319, which is in a Bartonian marine horizon in the Cowlitz Formation of Washington.

It was synonymized subjectively with Acila (Truncacila) decisa by Squires (1984) and Squires (1999).
Acila gabbiana was named by Dickerson (1916). It is a 3D body fossil. Its type locality is UCMP 1817, Urruttia Canyon-Salt Creek, which is in a Ypresian deep-water shale in the Lodo Formation of California.

It was synonymized subjectively with Acila (Truncacila) decisa by Vokes (1939) and Squires (1984).
Acila lajollaensis was named by Hanna (1927). Its type specimen is UCMP 31132 (neotype), a valve, and it is a 3D body fossil. Its type locality is UCR loc. 4922, which is in a Lutetian deep subtidal shelf shale in the Ardath Formation of California.

It was synonymized subjectively with Acila (Truncacila) decisa by Squires (1984).

Synonymy list

Year	Name and author
1855	Nucula decisa Conrad pp. 11 - 12 figs. pi. 2, fig. 19
1916	Acila gabbiana Dickerson p. 481 figs. pl. 36, fig. 1
1922	Nucula (Acila) stillwaterensis Weaver and Palmer p. 6 figs. pl. 8, fig. 8
1927	Acila lajollaensis Hanna p. 270 figs. pl. 25, figs. 1, 3, 5, 7-8, 12, 15.
1938	Acila (Truncacila) decisa Turner p. 41
1983	Acila (Truncacila) decisa Moore p. A10 figs. Plate 1, figure 14; plate 2, figures 1-3
1984	Acila (Truncacila) decisa Squires p. 41 figs. Figure 10a
1987	Acila (Truncacila) decisa Squires p. 54 fig. 86
1988	Acila (Truncacila) decisa Squires p. 17 fig. 44
1999	Acila (Truncacila) decisa Squires p. 22 figs. Figure 49

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Rank	Name	Author
kingdom	Animalia	()
—	Bilateria
—	Eubilateria	Ax 1987
—	Protostomia
—	Spiralia
superphylum	Lophotrochozoa
phylum	Mollusca
class	Bivalvia
—	Eubivalvia

Rank	Name	Author
subclass	Protobranchia	(Pelseneer 1889)
superorder	Nuculiformii	Dall 1889
order	Nuculida	(Dall 1889)
superfamily	Nuculoidea	(Gray 1824)
family	Nuculidae	Gray 1824
genus	Acila	Adams and Adams 1858
subgenus	Truncacila	Grant and Gale 1931
species	decisa	()

If no rank is listed, the taxon is considered an unranked clade in modern classifications. Ranks may be repeated or presented in the wrong order because authors working on different parts of the classification may disagree about how to rank taxa.

†Acila (Truncacila) decisa Conrad 1855

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Invalid names: Acila gabbiana Dickerson 1916 [synonym], Acila lajollaensis Hanna 1927 [synonym], Nucula (Acila) stillwaterensis Weaver and Palmer 1922 [synonym]

Diagnosis

Reference	Diagnosis
C. E. Weaver and K. Palmer 1922 (Nucula (Acila) stillwaterensis)	Shell small, rectangular in outline ; anterior dorsal margin nearly straight, posterior ventral margin nearly straight, sloping to a broadly rounded anterior end which approaches the dorsal margin with greater convexity ; escutcheon impressed but not defined by an incised line ; central portion of the area of the escutcheon raised, protruding slightly beyond the posterior margin; surface ornamented with radiating ribs medium in strength; above the central portion of the shell the divarication is single, below the mid-area the series of divarication is comparatively wide, the duplication increasing ventrad forming five sets along the ventral margin ; the area of divarication occupying the middle third of the ventral portion of the shell ; lunule not defined ; surface with heavy, impressed growth lines forming wide undulations on the surface of the shell.

Measurements

No measurements are available

Composition:

aragonitef

Entire body:

yesf

Adult length:

1.0 to < 10f

Adult width:

1.0 to < 10f

Adult height:

1.0 to < 10f

Thickness:

thinf

Folds:

nonef

Ribbing:

minorf

Spines:

nonef

Internal reinforcement:

nonef

Ontogeny:

accretionf

Environment:

coastal, inner shelf, outer shelf, oceanicf

Locomotion:

facultatively mobilef

Life habit:

infaunalf

Diet:

deposit feederf

Diet 2:

suspension feederf

Vision:

blindc

Created:

2008-11-15 10:09:53

Modified:

2009-08-18 20:13:53

Source: f = family, c = class

References: Aberhan et al. 2004, Mikkelsen and Bieler 2008

Age range: base of the Thanetian to the top of the Late/Upper Eocene or 59.20000 to 33.90000 Ma

Collections (48 total)

Time interval	Ma	Country or state	Original ID and collection number
Danian - Thanetian	66.0 - 56.0	Russian Federation	Acila decisa (49981)
Paleocene	66.0 - 56.0	USA (California)	Acila decisa (11117)
Thanetian	59.2 - 56.0	USA (California)	Acila decisa (52612 52613 52615 52617 52618)
Ypresian	56.0 - 47.8	USA (Washington)	Acila decisa (5544 5546)
Ypresian	56.0 - 47.8	USA (Oregon)	Acila decisa (52266 52267 52272 200799 200800 200802 200803 200804)
Ypresian	56.0 - 47.8	USA (California)	Acila decisa (193545 207305 207306 207308) Acila decisa, Acila gabbiana (122294) Acila gabbiana (122337 122339) Nucila gabbiana (52434)
Ypresian - Lutetian	56.0 - 41.3	USA (Oregon)	Acila decisa (37871)
Eocene	56.0 - 33.9	Russian Federation	Acila decisa (50129)
Lutetian	47.8 - 41.3	USA (California)	Acila decisa (5524 5532 5541 16712 178733 200853) Acila lajollaensis (200720)
Lutetian	47.8 - 41.3	USA (Oregon)	Acila decisa (200895 201033)
Lutetian - Bartonian	47.8 - 38.0	USA (Washington)	Acila decisa (43343 43346)
Lutetian - Bartonian	47.8 - 38.0	Russian Federation	Acila decisa (50126)
Middle Eocene - Late/Upper Eocene	47.8 - 33.9	USA (California)	Acila decisa (37930)
Middle Eocene - Late/Upper Eocene	47.8 - 33.9	USA (Washigton)	Acila decisa (203153 203154 203155 203156)
Middle Eocene - Late/Upper Eocene	47.8 - 33.9	USA (Washington)	Acila decisa (203152)
Bartonian	41.3 - 38.0	USA (Washington)	Nucula stillwaterensis (200105)
Bartonian	41.3 - 38.0	USA (Oregon)	Acila decisa (200863)
Priabonian	38.0 - 33.9	USA (Washington)	Acila decisa (202067)